Nowadays, no matter human life, scientific and technological activities and material production activities are inseparable from electricity. With the development of science and technology, some research contents with specialized knowledge have gradually become independent, forming specialized disciplines, such as electronics and electrotechnics. Electricity, also known as electromagnetism, is a basic subject of great significance in physics.
Basic contents of electricity
The contents of electrical research mainly include static electricity, magnetostatics, electromagnetic fields, circuits, electromagnetic effects and electromagnetic measurement.
Electrostatics is a subject that studies the electric field generated by electrostatic charge and its law of action on charge. There are only two kinds of charges, called positive charge and negative charge. Like charges repel each other, but different charges attract each other. Charge obeys the law of conservation of charge. Charge can be transferred from one object to another, and the algebraic sum of charge remains the same in any physical process. The so-called electrification is just the separation or transfer of positive and negative charges; The so-called charge disappearance is just the neutralization of positive and negative charges.
The interaction between electrostatic charges conforms to Coulomb's law: the magnitude of the interaction between two electrostatic charges in vacuum is directly proportional to their product and inversely proportional to the square of the distance between them; The direction of the force is along the line between them, charges of the same sign repel each other, and charges of different signs attract each other.
The interaction between charges is realized by the interaction of electric fields generated by charges. The electric field generated by charge is described by electric field strength (field strength for short). The electric field intensity of a point in space is defined by the electric field force of the positive unit probe charge at that point, and the electric field intensity follows the principle of superposition of field strengths.
Ordinary substances can be divided into two situations according to their different conductivity: conductor and insulator. There is movable free charge in the conductor; Insulators, also known as dielectrics, contain only bound charges.
Under the action of electric field, the free charge in the conductor will move. When the composition and temperature of the conductor are uniform, the condition to achieve electrostatic balance is that the electric field intensity inside the conductor is equal to zero everywhere. According to this condition, some properties of conductor electrostatic balance can be derived.
Magnetostatics is a subject that studies the magnetic field generated when the current is stable and the force of the magnetic field on the current.
The directional flow of charge forms an electric current. There is a magnetic interaction between currents, which is transmitted by a magnetic field, that is, currents generate a magnetic field in the space around them, and the magnetic field exerts a force on the current placed in it. The magnetic field generated by current is described by magnetic induction intensity.
Maxwell's equation describes the universal law of electromagnetic field. It can solve all kinds of macroscopic electrodynamics problems in principle by combining with the medium equation of matter, Lorentz force formula and charge conservation law.
An important result derived from Maxwell's equations is that electromagnetic waves exist and the changing electromagnetic fields propagate in the form of electromagnetic waves. The propagation speed of electromagnetic wave in vacuum is equal to the speed of light. This also shows that light is also an electromagnetic wave.
Circuits, including DC circuits and AC circuits, are all part of electricity. DC circuit studies the laws and properties of the circuit under the condition of constant current; Ac circuit studies the laws and properties of the circuit under the condition of periodic change of current.
The direct current path is formed by connecting conductors (or wires), and the conductors have a certain resistance. Under steady-state conditions, the current does not change with time and the electric field does not change with time.
According to the nature of steady electric field, the basic law of conduction and the concept of electromotive force, we can deduce various practical laws of DC circuit: ohm's law, Kirchhoff's circuit law, and some effective and simple theorems for solving complex circuits: equivalent source theorem, superposition theorem, reciprocity theorem, duality theorem and so on. These practical laws and theorems constitute the theoretical basis of circuit calculation.
There are electromagnetic induction and displacement currents, and there are electromagnetic waves.
The electrical effect in electromagnetic effect matter is the link between electricity and other physical disciplines (even non-physical disciplines). There are many kinds of electrical effects in matter, many of which have become or are gradually developing into specialized research fields. For example:
Electrostriction, piezoelectric effect (the electrical and electrical properties of dielectric transistors under mechanical pressure) and inverse piezoelectric effect, Seebeck effect, Peltier effect (at the junction of two different metals or semiconductors, heat is released when current passes in a certain direction and absorbed when current is reversed), Thomson effect (temperature gradient is maintained in metal conductors or semiconductors, heat is released when current passes in a certain direction and absorbed when current is reversed), Thermistor (resistance in semiconductor materials changes sensitively with temperature), photosensitive resistor (resistance in semiconductor materials changes sensitively with light), photovoltaic effect (potential difference caused by light in semiconductor materials) and so on.
The study of various electrical effects is helpful to understand the structure of matter and the basic processes that occur in matter. In addition, technically, they are also the basis for energy conversion and non-electrical measurement.
Electromagnetic measurement is also an integral part of electricity. The development of measurement technology is closely related to the theoretical development of this discipline, which promotes the improvement of measurement technology; The progress of measurement technology verifies the theory on a new basis and promotes the discovery of new theories.
Electromagnetic measurement includes the measurement of all electromagnetic quantities and other related quantities (frequency and phase angle of alternating current, etc.). Various special instruments (ammeter, voltmeter, ohmmeter, magnetic field meter, etc.). ) and measuring circuit, which can meet the measurement of various electromagnetic quantities.
Another important aspect of electromagnetic measurement is the electrical measurement of non-electric quantities (length, speed, deformation, force, temperature, light intensity, composition, etc.). Its main principle is to use some effect of the correlation between electromagnetic quantity and non-electric quantity to transform the measurement of non-electric quantity into the measurement of electromagnetic quantity. Because electrical measurement has a series of advantages, such as high precision, large range, small inertia, simple operation, long telemetry distance and automation of measurement technology, non-electrical measurement has been developing continuously.
Other branches of electricity
Magnetism, electricity, electrodynamics
Other branches of physics
Overview of physics, mechanics, heat, optics, acoustics, electromagnetism, nuclear physics and solid state physics.
History of electric power development
1. amber and magnets in BC
There is a philosopher named Thales among the seven sages of Greece. Around 600 BC, Thales saw the phenomenon that the Greeks of the Ming Dynasty attracted feathers by rubbing amber and attracted iron pieces with magnetic money ore, and once thought about the reasons. It is said that his explanation is: "Everything is animistic. Magnetism attracts iron, so magnetism has spirit. " The "magnetism" here is magnetite.
The Greeks called amber "elektron" (homophonic with English "electricity"). They import amber from the Baltic coast to make bracelets and jewelry. Jewelers at that time also knew that rubbing amber could attract feathers, but they thought it was the function of gods or magic.
In the East, China people had a knowledge of nature about magnets as early as around 2500 BC. According to Lu Chunqiu, China had a compass around 1000 BC, and they used a magnetic needle to tell the direction in ancient times.
2. Magnetism and static electricity
The so-called triboelectrification was only considered as a phenomenon in BC. For a long time, there has been no progress in understanding this phenomenon.
The compass has been used for navigation since 13. At that time, the compass put needle-like magnetite into straw and made it float on the water. /kloc-At the beginning of the 4th century, a navigation compass was made by hanging a magnetic needle with a rope.
This compass played an important role in 1492 when Columbus discovered the new continent of America and 15 19 when Magellan discovered the route around the earth.
(1) Magnetism, Electrostatic and Gilbert
Gilbert, an Englishman, is Queen Elizabeth's doctor. When he was a doctor, he also studied magnetism. He summed up the experimental results of magnetism for many years and published a book on magnetism in 1600. The book points out that the earth itself is a big magnet and expounds the magnetic inclination of the compass.
Gilbert also studied the phenomenon that friction amber attracts feathers, pointing out that this phenomenon exists not only in amber, but also in sulfur, fur, ceramics, wax, paper, silk, metal, rubber and other triboelectric substances. When two substances in this series rub against each other, the substance in front of the series will be positively charged and the substance in the back will be negatively charged.
At that time, the main research method was thinking, and he advocated that real research should be based on experiments. He put forward this idea and put it into practice. At this point, Gilbert can be said to be the pioneer of modern scientific research methods.
(2) Lightning and static electricity
In China BC, thunder was considered as an act of God. It is said that there are five immortals in charge of lightning. Their elder is Lei Zu, and under Lei Zu are Lei Gong and Dian Mu. Lei means that Lei Gong plays drums in the sky, and lightning means that Dian Mu uses two mirrors to shine light into the world below.
By Aristotle's time, it was more scientific. It is believed that the occurrence of thunder is due to the rise of water vapor on the earth, forming thunderstorm clouds, condensing into thunderstorms when encountering cold air, accompanied by strong light.
It was an Englishman who thought that thunder was static electricity, and that was in 1708. 1748, Franklin designed the lightning rod based on the same understanding.
Is there any way to collect this static electricity? This question has been considered by many scientists. 1746, Miao Sen Brooke, a professor at Leiden University, invented a bottle for storing static electricity, which later became the famous "Leiden bottle".
Miaosenbrook wanted to put electricity in a bottle just like water in a bottle. He first filled the bottle with water, and then put the glass cleaner into the water with a wire. Just as his hand touched the bottle and stick, he was given a heavy electric shock. It is said that he once said, "I don't want to do this terrible experiment again, even if it is ordered by the king."
Franklin wanted to store electricity in a Leyden bottle. 1752 In June, he did an experiment and put a kite in a thunderstorm. It is found that thunderstorm clouds are sometimes positively charged and sometimes negatively charged. This kite experiment is very famous, and many scientists are very interested and follow suit. 1753 In July, Russian scientist Lichtman was electrocuted in the experiment.
Professor from the University of Vodafone in pavia has proved that zinc, lead, tin, iron, copper, silver, gold and graphite are a series of metal voltages through experiments on various metals. When two metals in the series contact each other, the metal in the front row in the series is positively charged and the metal in the back row is negatively charged. He put copper and zinc as two electrodes in dilute sulfuric acid, thus inventing the voltaic cell. The voltage unit "Volt" is named after him.
/kloc-at the beginning of the 0/9th century, it was after the French Revolution that Napoleon entered the era. Napoleon came back from Italy. In 180 1 year, Volta was called to Paris to do electrical experiments. Volta was awarded the Gold Medal and Legino-Donoll Medal by Napoleon.
(3) The utilization of photovoltaic cells and the development of electromagnetism.
After the invention of the Volta battery, various countries have carried out various experiments and studies with this battery. Germany conducted research on electrolytic water, and British chemist David connected 2000 voltaic cells together and conducted an arc discharge experiment. David's experiment is to install charcoal on the positive and negative electrodes, adjust the distance between the electrodes, and make them discharge and emit strong light. This is the beginning of electric lighting.
1820 Oster, a professor at the University of Copenhagen, Denmark, published his findings in a paper: When a magnetic needle is placed next to a wire connected to a voltaic cell, the magnetic needle will immediately deflect.
Sillinger in Russia read this paper. He combined the coil with the magnetic needle and invented the telegraph (183 1), which can be said to be the beginning of the telegraph.
Later, Ampere of France discovered Ampere's law about the direction of magnetic field around current (1820), Faraday discovered the epoch-making electromagnetic induction phenomenon (183 1), and electromagnetism developed rapidly.
On the other hand, the research on circuits is also developing. Ohm discovered Ohm's law about resistance (1826), and Kirchhoff discovered the law about circuit network (1849), thus establishing electrotechnics.
3. The history of wired communication
Some people say that the development of science and technology is due to military needs, which has certain historical facts.
Afraid of Napoleon's attack, Britain used a truss communication machine to report the French army's movements to its own troops. Sweden, Germany, Russia and other countries have also established communication networks composed of such communication machines for military purposes, and it is said that they have invested huge budgets.
The idea of transforming this communication machine into an electric communication mode is probably the beginning of wired communication.
(2) Morse telegraph machine
1837, Morse telegraph machine was successfully developed in the United States, and the inventor was Morse, who is famous for Morse code. Morse code is a signal encoded by dots and dashes.
Morse originally wanted to be a painter, so he studied in London. 18 15 years, he listened to a lecture on telegraph given by Boston university professor Jackson on the boat back to the United States, and the idea of morse code and telegraph came into being. In order to lay the telegraph line, Morse established the electromagnetic telegraph company, and opened the telegraph service between new york-Boston, Philadelphia-Pittsburgh and Toronto-Buffalo-new york on 1846.
Morse's career was very successful, so he founded telegraph companies all over the United States, and the telegraph business gradually expanded.
1846, morse telegraph was equipped with an audio receiver, which was more convenient to use.
(3) Telephone and switch
1876 February 14, two American inventors, Bell and Gray, submitted their telephone patent applications respectively. Bell's application and Bigret's application arrived two hours earlier, so Bell got the patent right.
1878, Bell set up a telephone company to manufacture telephones and fully develop the telephone industry.
Since the development of telephone service, switches have been shouldering important tasks. Switches around 1877 are called summoning switches. When an operator receives a call request, he gives the call to another operator.
Later, after repeated improvement, the block diagram switch was developed, and then the automatic switching mode (1879) was developed.
189 1, Strowger automatic exchange was successfully developed. At this point, the desire of automatic exchange has been realized. After that, we continued our research and reached the present electronic exchange after several stages.
(4) Submarine communication cable
With the improvement of land communication network, people began to consider laying communication cables on the seabed to realize communication between countries across the sea. 1840, Wheatstone has considered the submarine cable.
There are many problems to be solved in submarine cables. The mechanical strength, insulation and laying methods of cables are different from those of onshore cables.
1845, the Straits Submarine Telegraph Company was established and started the submarine cable laying project from Britain to Canada and across the Dover Strait to France.
The laying of submarine cables has encountered major problems such as cable breakage, but laying submarine cables is the requirement of the times, and all countries have made contributions.
185 1 year, the earliest Calais-Dover submarine cable was laid, and communication was successfully realized. Taking this opportunity, many cables were laid in Europe and the eastern United States.
Now, the world's oceans are full of communication cables.
4. History of wireless communication
Information from anywhere in the world can be displayed on TV, which is brought to us by radio waves.
The earliest radio wave experiment was conducted by Hertz in Germany in 1888. Hertz found through experiments that electric waves, like light, have linear propagation, reflection and refraction.
The frequency unit hertz comes from his name.
(1) Marconi's radio equipment
Marconi, an Italian, read an article about Hertz experiment in a magazine, and developed the earliest radio device in 1895, and used this device to conduct Morse code communication experiments at a distance of about 3 kilometers. He thought of making wireless communication an enterprise, so he set up a wireless telegraph signal company.
Although Marconi has achieved a lot of success in the field of wireless communication, his intention to set up a wireless telegraph office in Newfoundland was opposed because of the conflict of interest with the submarine cable company, and Marconi's opponents were not few.
(2) wireless telephone
If it is not Morse signal but human language, then a carrier wave is needed to carry the signal. The carrier wave must be a high frequency wave.
1906, alexanderson of American General Electric (GE) Company made an 80KHZ high frequency signal generator, and successfully conducted the wireless telephone experiment for the first time.
In order to transmit voice by wireless telephone and listen to it, it is necessary to have a high-frequency signal generator for transmission and a detector for reception. Fessenden designed a multi-difference receiver and successfully tested it in 19 13.
Dader designed a receiver, with Paulson arc emitter as the transmitting device and electrolytic detector as the receiving device. At that time, due to the use of spark oscillator, the noise was very high, and the experimental stage was successful, but it was still far from practical use.
In order to make the generated radio waves stable and the received noise small, we have to wait for the appearance of electron tubes.
(3) Diodes and triodes
1903, Edison found that electrons splashed from the hot filament of the light bulb blackened a part of the light bulb. This phenomenon is called the Edison effect.
1904, Fleming was inspired by the Edison effect and made a diode for detection.
1907, USA d. Forest invented the triode by adding an electrode called the gate between the anode and cathode of the diode.
This kind of transistor can be used to amplify the signal voltage, and can also be matched with an appropriate feedback circuit to generate a stable high-frequency signal, which can be said to be an epoch-making circuit element.
After further improvement, the triode can generate high-frequency signals such as short wave and ultrashort wave. In addition, the triode has the function of controlling the electron flow, and the cathode ray tube and oscilloscope that followed are also closely related to this.
5. History of batteries
1790, galvani put forward "animal electricity" according to the experiment of dissecting frogs. From this, Volta discovered the law that two metals contact to generate electricity, which can be said to be the origin of the battery.
1799, Volta sandwiched a layer of paper saturated with salt water between copper and zinc, and then stacked them layer by layer to make a "Volta stack". A "stack" is a lot of single cells piled high together.
(1) main battery
A battery that can no longer be used after discharge is called a primary battery. Volta improved the Volta reactor and made a Volta battery.
1836, Daniel, an Englishman, put an anode and an oxidant in a ceramic bucket and made Daniel battery. Compared with Volta battery, Daniel battery can provide current for a long time.
1868, French Leclanche announced Leclanche battery, 1885 (Meiji 18), and Japanese tail well dry battery was invented by Kenzo. Tailwell dry battery is a kind of special battery that absorbs electrolyte in sponge, which has the characteristics of convenient handling.
19 17, Ferry of France invented the air battery, 1940, Rubin of the United States invented the mercury battery.
(2) Secondary battery
A battery that can be recharged after discharge is called a secondary battery. 1859, Plante of France invented the rechargeable lead battery. Its structure is that the lead electrode is installed in dilute sulfuric acid, which is the earliest secondary battery. Now, this kind of battery is used in cars.
1897 (the 30th year of Meiji), a lead-acid battery with a capacity of 10A*H was developed by Xuanzong of Shimadzu, Japan, and the prefix GS of his own name, Sima Zu, was put on the market as a commodity name.
1899 Sweden made the accommodation battery, 1905 Edison made the Edison battery. The electrolyte of these batteries is potassium hydroxide, which was later called alkaline batteries.
1948, Newman of the United States invented the nickel-cadmium battery. This is a rechargeable dry battery with epoch-making significance.
(3) Fuel cells
1939, the Englishman Grove discovered that the reaction between oxygen and hydrogen produced electricity, and proved the possibility of fuel cells through experiments. That is, when water is electrolyzed, electric energy is consumed and oxygen and hydrogen are generated. On the contrary, by externally supplying oxygen to the anode side and hydrogen to the cathode side, electric energy and water can be generated.
Grove only did experiments at that time, which was not practical. 1958, a 5KW fuel cell was made by the University of Cambridge, England.
1965, GE company of the United States successfully developed a fuel cell, which was installed on the manned spacecraft Gemini 5 in 1965 to provide the astronauts with electric energy for drinking water. 1Apollo 1 1 which landed on the moon in 1969 also used fuel cells as the power supply in the spacecraft.
(4) Solar cells
1873, Siemens, Germany invented a photovoltaic cell made of selenium and platinum wire. Now this kind of selenium photocell is used in the camera exposure table.
1945, Xia pin of the United States invented the silicon solar cell, which is an element that can generate electric energy when sunlight or light shines on its PN junction, and is widely used in satellites, solar cars, clocks, desktop calculators, etc. The research and development work to improve the conversion efficiency of this module is still in progress.
6. The history of lighting
65438+The industrial revolution in Britain in the 1960s brought the factory into the era of continuous processing and mass production, and night lighting became an important issue.
As mentioned earlier, the Englishman David 18 15 once made a famous experiment, using 2000 voltaic cells to generate an arc.
(1) incandescent bulb
1860, an Englishman Swan carbonized cotton thread and put it into a glass bulb to invent a carbon filament bulb.
However, due to the low vacuum technology at that time, the illumination time should not be too long. After a long time, the filament will oxidize and burn in the bulb.
Swan's idea about incandescent light bulbs is the origin of today's white woven lights. With the development of filament research and vacuum technology, incandescent lamps finally have practical uses. From this perspective, Swan's invention is a great invention.
1865, Sprengel developed a mercury vacuum pump to study the vacuum phenomenon. Knowing this, Swan improved the vacuum degree in the glass bulb at 1878 and made some efforts on the filament. He first treated cotton thread with sulfuric acid, then carbonized it, and finally, he announced the swan light bulb. Swan's incandescent bulbs are on display at the Paris World Expo.
1879, American Edison successfully extended the life of incandescent light bulbs to more than 40 hours. 1880, Edison discovered that bamboo is an excellent material for making incandescent filament, so he collected bamboo from Japan, China and India for repeated experiments.
Edison sent his subordinate Moore to search for high-quality bamboo in Hachiba, Kyoto, Japan. A few years later, he made a filament out of bamboo. He founded Edison Electric Company in London and new york in 1882 in order to make this kind of light bulb with bamboo filaments.
In Japan, Tokyo Electric Power Company was founded in 1886 (Meiji 19). Since the 22nd year of Meiji, ordinary families began to use white light bulbs.
19 10 years, Cooley Hall in the United States used tungsten wire and invented the tungsten wire bulb.
19 13, Langmuir of the United States filled the glass bulb with gas to prevent the filament from evaporating, and invented the inflatable tungsten filament bulb.
1925, Bubu Tangsan of Japan invented the inner wall frosted light bulb.
1932, Japanese Mihura Junyi invented the double helix tungsten filament bulb.
It is precisely because of the above-mentioned continuous exploration that we can enjoy the daily life of incandescent lighting today, which is really a long way to go.
(2) Discharge lamp
1902, Huyzt of the United States put mercury vapor into a glass bulb and invented an arc discharge mercury lamp. This kind of mercury lamp is often used as a germicidal lamp because it emits more ultraviolet rays when the pressure of mercury vapor is low. When the pressure of mercury is high, it can emit strong visible light.
At present, the light emitted by high-pressure mercury lamps, which are widely used in square lighting and road lighting, is a kind of mixed light, including the light emitted by mercury arc discharge and the light emitted by ultraviolet rays irradiated on fluorescent materials coated on the inner wall of glass shells.
1932, Philips of the Netherlands developed a monochromatic sodium lamp with a wavelength of 590nm, which is widely used for highway tunnel lighting.
1938, Inman of the United States invented the fluorescent lamp which is widely used now. This lamp emits different colors of light by irradiating different phosphors coated on the inner wall of the lamp tube with ultraviolet rays emitted by mercury arc discharge. Generally, white fluorescent lamps are used the most.
7. History of power equipment
It can be said that the electromagnetic action discovered by Oster in 1820 is the origin of the motor.
The electromagnetic induction discovered by Faraday at 183 1 is the origin of the transformer of the generator.
(1) generator
1832, the Frenchman Bi Ke West invented the handheld DC generator. Its principle is to change the magnetic flux by rotating the permanent magnet, generate induced electromotive force in the coil and output this electromotive force in the form of DC voltage.
1866, Siemens of Germany invented the self-excited DC generator.
1869, Belgium made a ring armature and invented a ring armature generator. This kind of generator uses water power to turn the rotor of the generator. After repeated improvement, it was obtained in 1847. 2KW output power.
1882, Gordon of the United States made a two-phase giant generator with an output of 447KW, a height of 3 meters and a weight of 22 tons.
Tesla of the United States was determined to develop AC motors when he was in Edison Company, but Edison insisted on DC mode only, so he sold the patent rights of two-phase AC generators and motors to Westinghouse Company.
1896, Tesla's two-phase alternator began to operate in Nyala Power Plant, and 3750KW and 5000V alternating current was sent to Buffalo, 40 kilometers away.
1889, Westinghouse built a power plant in Oregon, 1892, and it successfully sent 15000 volts to Pittsfield.
(2) Motor
1834, Russia's Jacobi trial-produced a DC motor composed of electromagnets. 1838, this kind of motor started a ship, and the power supply of the motor used 320 batteries. In addition, Winport in the United States and Derbyson in the United Kingdom also built DC motors (1836) as power equipment for printing machines. Because these motors are powered by batteries, they are not widely used.
1887, Tesla two-phase motor mentioned above was started as a development plan of practical induction motor. 1897, Westinghouse made an induction motor and set up a professional company to promote the motor.
(3) Transformer
When the power generation terminal transmits alternating current to the outside, it is necessary to increase the alternating voltage first, and then reduce the transmitted alternating voltage at the power consumption terminal. Therefore, the transformer is essential.
183 1 year, Faraday found that magnetism can induce electricity, which is the basis for the birth of transformers.
1882, Gibbs of Britain obtained the patent of "Lighting and Power Distribution Mode", the content of which is to use transformers for power distribution. The transformer used at that time was an open magnetic circuit transformer.
Westinghouse imported Gibbs' transformer and developed a practical transformer in 1885 after research.
In addition, the previous year's 1884, Hopkinson of Britain made a closed magnetic circuit transformer.
8. History of electronic circuit components
Nowadays, electronics, including computers, are very prosperous, and its background is closely related to the continuous development of electronic circuit components from tube-transistor = integrated circuit.
(1) electron tube
The electron tube was invented in the order of diode-triode-quadrupole-pentode.
Diode: As mentioned above, Edison discovered the "Edison effect" of the light bulb filament emitting electrons. 1904, the Englishman Fleming was inspired by the Edison effect and invented the diode.
Triode: 1907, forest of the United States invented the triode. At that time, the vacuum technology was immature and the manufacturing level of triode was not high. However, in the process of repeated improvement, people understand that triode has amplification function, and finally the curtain of electronics has been opened.
The oscillator has also developed from the Marconi spark device mentioned above to the triode oscillator. A triode has three electrodes, an anode, a cathode and a control grid arranged between them. The control grid is used to control the electron flow emitted by the cathode.
Pentode: 1927, Jobst added another electrode between the anode and the curtain grid, and invented the pentode. The newly added electrode is called the suppression grid. The reason why this electrode is added is that when the electron current hits the anode in the quadrupole, the anode will produce secondary electron emission, and the suppression grid is set to suppress this secondary electron emission.
In addition, in 1934, Thomson of the United States invented the acorn tube suitable for ultrashort wave by improving the miniaturization of the electron tube.
1937 invented the ST tube with metal shell instead of glass, and 1939 invented the miniaturized MT tube.
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